Hi Siva,

Does PWA store the user preferences like it happens in native apps?

I feel, we can implement this feature using localstorage , webdb or session storage. PWA is just tech which allow you to use web app as native application. it provide way to add your web app as installable, no address bar etc.
What is the memory foot print of PWA apps?

PWA are web-apps , so memory taken by your browser + memory take by your web-application.

Is there anything that PWA can not do what native app can do?

PWA app cannot access native OS . to Access them we need to add cordova or any other tech. and provide installable.

Are all browsers support PWA? firefox? safari??

yes, it becoming standard now. though for apple, os version should be ios 11.3 or 12.

is the interaction between PWA app and native app seamless?

if app is made with latest tech like reactjs , angular with performance in mind, it provide good user experience. but as of now it is not as seamless as native.